New system for processing particles (moving flows of bodies).
It is based on ChParticleProcessor. One can plug into this processor object two components:
- a ChParticleEventTrigger (there are a few children classes, ready to use; ex. trigger when entering a box)
- a ChParticleProcessEvent  (there are a few children classes, ready to use; ex. remove from simulation, count, etc.)
More will be added in future.